An organic light-emitting diode (OLED) is an organic thin film electroluminescent device and has the advantages such as simple preparation process, low cost, high luminous efficiency, capability of conveniently forming a flexible structure and the like. Therefore, the display technology using OLED has become an important display technique.
Currently, the methods for forming an organic electroluminescent layer in the OLED are as follows: (1) the vacuum evaporation method which is applicable to small organic molecules, has the characteristic of not requiring a solvent in the process of forming the organic electroluminescent layer and having a uniform film thickness, suffers high equipment investment and low material utilization, and is not applicable to the production of large-size products; and (2) methods such as spin coating, inkjet printing, nozzle coating method and the like adopting a solution of organic electroluminescent materials. The methods are applicable to polymer materials and soluble small molecules, have the characteristic of low equipment cost, and are outstanding in the large-scale and large-size production. Particularly, in the inkjet printing technology, the solution can be accurately sprayed into a pixel region to form an organic electroluminescent layer, but the maximum problem of the inkjet printing technology lies that: the solution of the organic electroluminescent materials cannot easily form the organic electroluminescent layer with uniform thicknesses in the pixel region.
Japanese patent JP2008243406 discloses a method for preparing an OLED, in which a PDL has two layers: the first layer (the lower layer) is made of an inorganic hydrophilic material (the hydrophilic material is adsorbable to a solution of an organic electroluminescent material), and the second layer (the upper layer) is made of an organic hydrophobic material (the hydrophobic material is repellent to the solution of the organic electroluminescent material); by adoption of the PDL made of two layers of materials of different wettabilities, accurate inkjet printing can be performed on the solution of the organic electroluminescent material to form an organic electroluminescent material film with uniform thickness; and when the PDL is prepared, an inorganic hydrophilic material layer must be prepared at first; an organic hydrophobic material layer is prepared on the inorganic hydrophilic material layer; and then the PDL is prepared by the two layers of materials by a patterning process. Meanwhile, European patent EP0989778A1 discloses a method for forming a PDL in a two-layer structure on a substrate. By treatment with plasmas, the first layer (the lower layer) has high surface energy (hydrophilic material), and the second layer (the upper layer) has low surface energy (hydrophobic material), and then the requirements on accurate inkjet printing and film uniformity can also be met.